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Urban Stream Ecology: 3 Portland Streams

author: Maria Chloë Hawsadvisor: Robert Kaplanyear: 1985

ABSTRACT: The River Continuum Concept states that from the headwaters to the mouth of a river, a continuously varying gradient of physical conditions is present. Since biological communities are structured by their habitats, a similar continuum should exist for them as well (an ecocline). Three low-order, urban streams were studied to determine if their habitats and biological communities varied according to the Concept's predictions. It was found that the trophic basis of the ecosystem (detritus) was present in the proportions predicted. The headwater streams, Reed Canyon and Crystal Springs, were dominated by coarse particulate organic matter while the downstream reach (Johnson Creek) contained a larger percentage of finer particles. The results of a leaf decomposition study demonstrated that leaves decomposed fastest in the headwaters areas where organisms which exploit terrestrial inputs are already present in large numbers. In a community analysis of the macroinvertebrate populations, Reed Canyon, and to a lesser extent, Crystal Springs, contained populations typical of undisturbed natural streams. However, reduced species diversity, lower biomass, lower species richness and a larger number of pollution tolerant species at Johnson Creek led to the conclusion that it is experiencing environmental stress, perhaps in the form of pollution.